1. Field of the Invention
The present invention relates to a brake band used in an automatic transmission of, for example, a motor vehicle. More particularly, the present invention relates to a brake band in which a friction plate to be attached to a strap is provided with a groove.
2. Related Background Art
In general, a brake band comprises an annular strap cut transversely at one location, brackets provided on cut ends the strap and a friction material secured to an inner peripheral surface of the strap and is designed so that so that the strap is tightened against a drum by applying a force to the apply side bracket by means of an apply pin, thereby obtaining a braking force.
Japanese Utility Model Application Laid-open No. 05-047559 discloses a brake band in which a lining disposed on an inner periphery of a strap is provided with a groove to prevent transmission shock during the braking. Further, Japanese Utility Model Application Laid-open No. 63-135031 (1988) discloses a brake band in which a plurality of grooves extending in a circumferential direction are formed in a lining disposed on an inner peripheral surface of a strap, at an apply portion and/or an anchor portion or through the whole circumferential direction.
In general, in an attachment condition in which the loading of an anchor pin directs from an upward direction to a downward direction upon releasing the brake band, during an idle rotation in a normal direction, by the dropping of the brake band due to its own weight and by self winding (mechanical property of the brake band) toward an anchor side, the brake band tends to be pulled toward a rotational direction. Thus, clearance between an upper part of a drum and the brake band is decreased to a maximum extent, and drag torque reaches a peak value at or around 2000 rpm under various conditions. As a result, the great dragging torque acts on the band drum and the drag torque is increased under a high rotational condition that occurs most frequently due to the performance of the band, effect of automatic transmission and reduction of a fuel consumption rate are required. Further, regarding the above explanation, this is also true when the drum is rotated in a reverse direction in an attachment condition in which the loading of the anchor pin directs from the downward direction to the upward direction.
In order to solve such problems, there have been proposed techniques in which the groove(s) is/are provided in the lining or friction material as disclosed in the above-mentioned Japanese Utility Model Application Laid-open No. 05-047559 and Japanese Utility Model Application Laid-open No. 63-135031. However, in these patent documents, the groove(s) is/are provided in the friction material through the whole circumferential direction or at the apply portion and/or anchor portion.
For example, when the grooves are provided through the whole circumferential direction of the strap, it is feared that the dropping of the band cannot be suppressed completely.